Abstract:
Hengluanshan Formation volcanic rocks mainly distribute in the Hongshantou area, which is located in the south of Hongliuhe-Niujuanzi-Xichangjing suture belt. The authors researched Hengluanshan Formation volcanic rocks through zircon isotopes dating and geochemical analysis. The results show that the volcanic rocks are rich in LREE, lack HREE, and have not significantly negative europium anomaly. The REE patterns of the volcanic rocks are similar to the typical high-magnesium andesite of the Setouchi volcanic belt in Japan. There is higher MgO content (2.85% to 4.13%) and lower FeO
T/MgO value (0.75 to 1.2, less than 1.5) in the volcanic rocks. The Al
2O
3 content is from 5.59% to 17.15%, and the CaO content is less than 10% (5.97% to 8.30%). The volcanic rocks have the geochemical characteristics of analogy high-magnesium andesite. So, the authors considered that Henluanshan Formation volcanic rocks formed at the early stage of Beishan oceanic crust subduction. The zircon U-Pb age of Henluanshan Formation volcanic rocks is (453.5±2.7) Ma, and it indicates that Beishan ocean subducted at the early stage of Late Ordovician.